CN113056566A

CN113056566A - Carbon increasing material and carbon increasing method using same

Info

Publication number: CN113056566A
Application number: CN201980075578.4A
Authority: CN
Inventors: 宗冈均; 浅原纪史; 坂元基纮; 山崎强
Original assignee: Nippon Steel and Sumitomo Metal Corp
Current assignee: Nippon Steel Corp
Priority date: 2018-12-07
Filing date: 2019-12-06
Publication date: 2021-06-29
Anticipated expiration: 2039-12-06
Also published as: KR102517013B1; KR20210079354A; BR112021010228B1; WO2020116643A1; BR112021010228A2; US20210404047A1; TW202035706A; JP6954481B2; JPWO2020116643A1; CN113056566B

Abstract

A carburizing material and a carburizing method using the same, the carburizing material is a carburizing material for carburizing molten iron accommodated in an electric furnace or a ladle, and is a carbon material with an ash content of 5% to 18% by mass Mixture with quicklime, and satisfy the conditions of 0.6≤(mc+Mc)/ms≤2.7 and 0.7≤(mc+Mc)/ma≤6.5. Here, mc represents the mass of CaO in the carbon material, ms represents the mass of SiO ₂ in the carbon material, ma represents the mass of Al ₂ O ₃ in the carbon material, and Mc represents the mass of the quicklime.

Description

Carbon increasing material and carbon increasing method using same

Technical Field

The present invention relates to a carburization material for efficiently carburizing in an electric furnace or a ladle, and a carburization method using the same.

Background

Conventionally, cold iron sources such as iron scrap, pig iron, and direct reduced iron are melted and refined in an electric furnace to produce steel materials used for building materials and the like. The electric furnace uses an auxiliary heat source such as oxygen (for oxidizing and melting iron), gas fuel, liquid fuel, and powdered coke, for the purpose of promoting melting and refining and saving expensive electric energy.

In addition, the following steps are also carried out: a solid carbon material is added to molten iron as a recarburizing material to recarburize the molten iron, and oxygen is used as an auxiliary heat source to combust carbon in the molten iron. The carbonaceous material used is artificial graphite, soil-like graphite, various cokes, smokeless carbon, wood, or a material produced from these materials. In the smelting reduction method, a large amount of coal is generally charged together with iron ore and an oxidizing gas to reduce the iron ore, but in order to produce high-carbon steel in a ladle, auxiliary carburization may be performed.

As a carburization material or a carburization technique thereof, for example, patent document 1 discloses a carburization material for iron making or steel making obtained by firing earthy graphite having an ash content of less than 12 mass%, and patent document 2 discloses a carburization technique characterized by adding earthy graphite. Patent document 3 discloses a carbonized material obtained by dry distillation of coconut shells of coconut or oil coconut as an alternative to coke. Patent document 4 discloses a technique of adding a carbon source derived from biomass as a technique of carburizing in dephosphorization.

When iron scrap is used as a chill source in an electric furnace, carbon injection and oxygen enrichment operations are generally performed, and a carburized material is transported to an injection gas and injected into molten iron. On the other hand, if the additive can be fed from above the furnace by free fall, not only the facility for gas conveyance can be omitted, but also the restrictions on the particle size of the additive and the like can be alleviated, and the cost can be reduced. In addition, when direct reduced iron is used as a cold iron source in addition to iron scrap, and when low-grade direct reduced iron having a low metallization ratio is used, a carbon source for reduction is required in addition to a carbon source as a heat source, and a large amount of carburization is required. Further, in order to produce a low-N high-grade steel, carburization is required for N removal during decarburization, and if carburization can be efficiently performed at low cost, a high-grade steel can be produced at low cost.

Generally, if an inexpensive carbon material in which a large amount of ash is mixed can be used, the cost can be kept low, but if the ash content in the carbon material is high, it is not preferable in many methods of use. It is generally known that the recarburisation rate becomes significantly slower at high ash contents. Here, the recarburization rate is a rate at which the carbon concentration in the molten iron increases in a state where a carbon source is added to the furnace. For example, patent document 1 shows: although the earthy graphite having an ash content of less than 12% by mass can achieve a recarburization (recarburization rate) equivalent to that of the artificial graphite, the recarburization rate is significantly reduced for a recarburization material having an ash content exceeding that. Patent document 4 shows that the higher the ash content, the lower the recarburization rate, and that the ash content is set to 9 mass% or less in the recarburizing material. It is believed that: the reason why the recarburization rate becomes slow if the ash content is high is that components derived from ash coat the carbonaceous material.

On the other hand, a carbon material obtained by adding an additive to a carbon material, and a method of carburizing using the same have been proposed. For example, patent document 5 discloses the addition of CaF to powdery smokeless carbon₂And MgO and briquetted to form the block-shaped smokeless carbon. However, at present, fluorine-free materials are required as by-products due to problems such as elution of fluorine from slag, and use thereof is limited. Patent document 6 discloses a recarburizing material in which 20 mass% or more and less than 80 mass% of CaO is mixed with a carbon material, but the cost increases because the proportion of CaO is large. Further, patent document 7 discloses a method of adjusting CaO/C in RH type vacuum degassing treatmentThe mass ratio of (2) is adjusted to 18 or more, and a top-blown additive of a carbon additive is added, but this method also has a problem of a large proportion of CaO, and in addition, the range of increase in carbon concentration in molten steel is in the range of 0.005 to 0.010 mass%, which is greatly different from the production of molten iron in a general electric furnace.

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication No. 55-38975

Patent document 2: japanese laid-open patent publication No. 1-247527

Patent document 3: japanese patent laid-open publication No. 2009-46726

Patent document 4: japanese patent laid-open publication No. 2013-72111

Patent document 5: japanese patent laid-open publication No. 2004-76138

Patent document 6: japanese patent laid-open publication No. 2003-171713

Patent document 7: japanese patent laid-open publication No. 2013-36056

Patent document 8: japanese patent laid-open publication No. 2016-151036

Patent document 9: japanese patent No. 5803824

Disclosure of Invention

Problems to be solved by the invention

If an inexpensive carbon material containing a large amount of ash is used as the recarburizing material under a condition of weak stirring strength as in an electric furnace, the recarburizing rate may be reduced as described above. The inventors of the present invention have recognized that: even if the stirring strength is weak as in an electric furnace, the recarburization rate is reduced even at an ash concentration lower than that shown in patent document 1, and the influence of the ash concentration becomes remarkable at about 5 mass% or more. On the other hand, if the efficiency (i.e., the rate of carbon increase) in the case of using a carbon material having a high ash content can be increased to or above that conventionally recognized, an inexpensive carbon material can be used with high efficiency, and therefore, this is preferable. For this purpose, the following measures are required: the film formed on the carbonaceous surface by the ash in the carbonaceous material is removed to promote the recarburization. In addition, when the carburization material is charged by free fall, unlike powder supply by injection or bottom blowing, since the contact area between molten iron and the carburization material is reduced, the carburization rate is reduced, and there is a possibility that the carburization rate is reduced by introduction into slag or scattering before melting.

The present application has been made in view of such circumstances, and an object thereof is to provide a low-cost and highly efficient carbon material and a carbon increasing method using the same.

Means for solving the problems

The present inventors have made extensive studies to solve the above problems, and as a result, they have found that: by adding quicklime to the carbon material, the influence of ash film on the carbonaceous surface can be reduced. Additionally, it is also recognized that: the proper amount of quicklime depends on the SiO in the ASH (sometimes referred to as "ASH" in this application)₂And Al₂O₃The content of (b) varies.

The subject matter of the present application is as follows.

<1> a recarburizing material for recarburizing molten iron contained in an electric furnace or a ladle,

the carbon material is a mixture of carbon material and quicklime, the carbon material having an ash content of 5 to 18 mass%, and the carbon material satisfies the following conditions of formula (1) and formula (2).

0.6 ≤ (Mc + Mc)/ms ≤ 2.7 formula (1)

0.7 ≤ (Mc + Mc)/ma ≤ 6.5 formula (2)

Wherein mc represents the mass of CaO in the carbon material, and ms represents SiO in the carbon material₂Ma represents Al in the carbon material₂O₃Mc represents the mass of the quicklime.

<2> the carbon additive according to <1>, wherein the mixture satisfies the conditions of the following formulae (1A) and (2A).

0.6 ≤ (Mc + Mc)/ms ≤ 1.9 formula (1A)

0.7 ≤ (Mc + Mc)/ma ≤ 5.0 formula (2A)

<3> a recarburization method using the recarburizing material according to <1>, wherein the recarburizing material is added to the electric furnace or the ladle toward a molten iron surface formed by stirring the molten iron while blowing gas.

<4> the method according to <3>, wherein the additive is added by charging the additive from a lance toward the molten iron surface.

Effects of the invention

According to the present application, a low-cost carbon additive having excellent reaction efficiency and a carbon-adding method using the same can be provided.

Drawings

Fig. 1 is a diagram for explaining a process of charging a carburization material from above using an arc type electric furnace to perform carburization.

FIG. 2 shows CaO and SiO in the additive for each carbon material₂A graph of the relationship between the ratio C/S of (A) and the capacity coefficient.

FIG. 3 shows CaO and Al in the additive for each carbon material₂O₃A graph of the relationship between the ratio C/A of (A) and the capacity coefficient.

FIG. 4 shows CaO-SiO₂-Al₂O₃Graph of the magnitude of the carburetion rate on the ternary system state diagram.

FIG. 5 shows CaO and SiO in the carbon additive at different stirring power densities₂A graph of the relationship between the ratio C/S of (A) and the capacity coefficient.

FIG. 6 shows CaO and Al in the carbon additive at different dynamic densities of stirring₂O₃A graph of the relationship between the ratio C/A of (A) and the capacity coefficient.

Detailed Description

Hereinafter, embodiments of the present application will be described with reference to fig. 1.

As shown in fig. 1, in the case of carburizing the molten iron, in the electric furnace 1 with the bottom-blowing tuyere 4, the carburization material is supplied from above the molten iron 5 using a separate lance 3 different from the electrode 2, and the molten iron is stirred by flowing the stirring gas from the bottom-blowing tuyere 4.

It is believed that: the carbon material is charged into molten iron contained in an electric furnace or a ladle, and has the following effects: temperature rise of carbon material, and carbon content from surface of carbon materialWhile the surface is melted, ash films are formed on the surfaces of the carbonaceous materials by the ash remaining after melting, and the contact between the carbonaceous materials and molten iron is prevented, thereby reducing the carburization rate. The ASH content (ASH) in the carbon material is mainly SiO₂And Al₂O₃When both are added together, most of the carbon species account for 70% or more, and often about 90% or so of the ash content.

The present inventors analyzed an ash film formed when such a carbon material was added to molten iron from above by an electron microscope and X-ray analysis. The results thereof recognize that: the composition of the ash film does not necessarily coincide with the composition of ash in the carbon material. It is recognized that: in particular SiO in the ash₂Most of which are reduced, and the ash film mostly becomes to contain a large amount of Al₂O₃High melting point compounds of (2). Such compounds are mainly, for example, Al having a melting point of 1800 ℃ or higher₂O₃、CaO·6Al₂O₃Spinel (MgO. Al)₂O₃) Such a component. Further, if a recarburizer material in which quicklime powder is previously added to a carbon material and mixed is used, calcium silicate is formed to form SiO while adding CaO to the ash film₂The reduction of (a) is suppressed. It is recognized that: as a result, the composition of the ash film changes, and the composition approaches the composition expected from the analysis value of the carbon material and the amount of quicklime added, and changes in the direction in which the liquidus temperature decreases.

In addition, it is known that: although sulfur is often contained in a carbon material derived from natural sources, sulfur in molten iron has an effect of inhibiting contact of carbon atoms with molten iron and reducing the carburization rate. On the other hand, the inventors of the present invention conducted experiments and found the following results: when a carburized material in which quicklime is added to a carbon material is used, the rate of increase in the sulfur concentration in molten iron during carburization decreases as compared with the case where quicklime is not added. In addition, the desulfurization behavior is not limited to a vacuum furnace or a closed furnace, and is also similar to that in a normal atmospheric furnace if the desulfurization is performed without active supply of an oxidizing gas such as oxygen or air. This is believed to be due to: by adding quicklime powder and mixing in advance, C in the carbon material is brought close to CaO, and a reducing atmosphere is formed in the vicinity of the metal-slag interface.

By using a carburant in which a carbon material is mixed with quicklime in this manner, the following effects can be expected: the composition of the ash film formed on the surface of the molten iron or the carbon material is changed to prevent the decrease of the recarburization speed; and the reaction interfacial area is increased by local desulfurization of the molten iron surface.

Next, various experiments were performed in order to optimize the amount of quicklime to be mixed. The types of carbon materials used in this experiment are shown in table 1 below.

[ Table 1]

The moisture, ASH (ASH), volatile matter, and fixed carbon content ("%" is "mass%") in the carbon materials shown in table 1 were measured by JIS M8812: 2006, specifically, measured by the following method.

Moisture content: the weight loss when 5g of a sample pulverized to a particle size of 250 μm or less was dried at 107. + -. 2 ℃ until it became constant.

ASH (ASH): the content (% by mass) of the residue obtained when sample 1g was subjected to heat ashing at 815. + -. 10 ℃ was calculated as a percentage of sample 1 g.

Volatile components: the sample 1g was placed in a platinum crucible with a lid, and heated at 900. + -. 20 ℃ for 7 minutes while shutting off air, and the amount of water was removed from the weight loss.

Fixing carbon points: the fixed carbon fraction (mass%) is 100- (moisture (mass%), ash (mass%), volatile matter (mass%).

In addition, the composition of ash in the carbon material is defined by JIS M8815: 1976, and specifically, it is determined by the following method. In addition, SiO₂、Al₂O₃And CaO represents mass% in the ash.

SiO₂: melting the sample with sodium carbonate, dissolving the melt in hydrochloric acidThe silicic acid is dehydrated by perchloric acid treatment, filtered and the precipitate is stored. Silicic acid in the filtrate is recovered, and subjected to strong thermal ashing together with the main precipitate to prepare anhydrous silicic acid, and hydrofluoric acid and sulfuric acid are added to volatilize silica, thereby determining the amount of silica loss.

Al₂O₃: the sample was decomposed with hydrofluoric acid, nitric acid and sulfuric acid, and melted with potassium pyrosulfate. Dissolving the melt in hydrochloric acid, adjusting pH with acetic acid and ammonia water, and extracting with DDTC and chloroform to remove heavy metals. Adding a certain amount of EDTA standard solution to generate EDTA-aluminum complex salt, and carrying out back titration on the excessive EDTA by using the zinc standard solution.

CaO: the filtrate and washing liquid at the time of quantification of silica were collected, and a solution obtained by melting and dissolving the residue after quantification of silica in hydrochloric acid with sodium pyrosulfate was combined, and iron, aluminum, and the like were precipitated as hydroxides with ammonia water and filtered off. The pH of the solution was adjusted to precipitate magnesium hydroxide, the interfering components were masked with potassium cyanide, and titration was performed with EDTA standard solution using NN indicator.

The inventors of the present invention performed a test for measuring the carburization rate after adding a carburization material by controlling the bottom-blowing flow rate of bottom-blowing gas stirring using a 2 kg-scale small melting furnace and adding the carburization material while maintaining a predetermined molten iron temperature. First, quicklime powder was mixed with 6 kinds of carbon materials shown in table 1 to prepare a powdery carbon additive. Thereafter, the electrolytic iron was melted in a small melting furnace, the carbonaceous material was dropped onto the molten iron surface from above, bottom-blown gas stirring was performed, and sampling was performed at appropriate time intervals to determine the temporal change in the carbon concentration in the molten iron. The addition ratio of the quicklime powder is changed within the range of (the mass of the quicklime powder)/(the mass of the carbon additive) from 0.05 to 0.25. The behavior of the recarburization rate is assumed to be a primary reaction in which the difference between the saturated C concentration and the C concentration in the molten iron is used as a driving force, and the capacity coefficient K in the following equation (3) is set to a constant value, and the capacity coefficient K (1/s) is calculated. Here, C_S、C_t、C₀All the C concentrations in the molten iron (% by mass)_SMeans the saturated C concentration, C_tRefers to the C concentration at time t(s)，C₀Refers to the C concentration at time t equal to 0.

ln((C_S-C₀)/(C_S-C_t) K × t formula (3)

The capacity coefficient K defined in equation (3) is an index of the reaction efficiency of the carbonaceous material, and can be determined as follows: the larger the capacity coefficient K, the higher the recarburization rate of the recarburizing material and the more excellent the reaction efficiency.

The particle size of the carbon additive was uniformly in the range of 1.0. + -. 0.4mm by sieving. The bottom-blown gas agitation was performed in a range of 0.02 to 0.30 in terms of an agitation power density ∈ (kW/ton) calculated by the following formula (4). The range of the stirring power density is set to a value that is practical for use as an electric furnace or ladle.

ε＝371×Q×(T+273)/V×{ln(1+ρ×g×L/P)+1-(T_n+273)/(T +273) } formula (4)

In formula (4), Q: total flow rate (Nm) of bottom-blown gas³S), T: temperature of molten iron (. degree. C.), V: volume of molten iron (m)³) ρ: molten iron density (kg/m)³) G: acceleration of gravity (m/s)²) L, L: flying height (m) of blown gas, P: pressure (Pa), T of the atmosphere_n: the temperature (. degree.C.) of the gas blown in. In the test of the small melting furnace, L is the molten iron depth of the small melting furnace.

In the test using the small melting furnace, the test was performed while keeping the temperature T of the molten iron at 1400 ℃ ± 20 ℃. As described above, the ash film when quicklime powder is not added mainly consists of a large amount of Al₂O₃The high melting point composition of (2) is a composition which does not melt even at 1700 ℃ or 1750 ℃ which is a substantial upper limit of the temperature generally used in an electric furnace. For the purposes of this application, the ash film is controlled to be CaO-SiO by mixing quicklime powder in the carbon material₂-Al₂O₃However, the composition range in which the liquidus temperature is 1350 ℃ or less among the three components is very narrow, and when the ash composition in the carbon material varies from particle to particle, it is difficult to stably control the amount of quicklime to be added so as to have a composition in which the ash film is melted.

Then, as a realistic temperature that can be stably applied, a temperature near 1400 ℃ was selected and evaluated based on 1400 ℃. Since the composition becomes a liquid phase in a wider range than the above temperature, the viscosity also decreases, and therefore, if the amount of quicklime added is in the range of 1400 ℃, the molten iron temperature exceeding 1400 ℃ is effective. Under relatively high temperature conditions such as 1600 ℃, the same effect may be exhibited by a wider range of the amount of quicklime added, but by setting the composition to such a composition that the effect is exhibited at 1400 ℃, the fluidity becomes higher, and a significant reaction promoting effect can be expected. From the viewpoint of actual refractory wear, the molten iron temperature is preferably 1750 ℃ or lower, and more preferably 1700 ℃ or lower. In addition, there may be a local high-temperature place such as an arc point or a fire point by a top-blown oxygen lance. The temperature of the reaction part should be used as the molten iron temperature in principle, but since there is a problem in the measurement property or uniformity of the temperature distribution in practice, the average molten iron temperature as a whole may be substituted.

First, fig. 2 and 3 show the experimental results when ∈ is 0.08 ± 0.01 kW/ton. Wherein, if the ratio ({ Mc + Mc }/M) of the sum of the mass (Mc) of CaO in the ash content of the carbonaceous material and the mass (Mc) of quicklime to the mass (M) of the carbonaceous material is C, SiO in the ash content is set to C₂The ratio (ms/M) of the mass (ms) of (A) to the mass (M) of the recarburizing material is S, and Al in the ash is added₂O₃When the ratio (ma/M) of the mass (ma) of (b) to the mass (M) of the recarburizing material is A, C, S, A represents CaO and SiO contained in the recarburizing material, respectively₂、Al₂O₃The ratio of (a) to (b). The ratio of each component in the ASH contained in the carbon material is set as the product of the ASH ratio in the carbon material and the ratio of each component in ASH.

In fig. 2, the abscissa axis represents the ratio C/S (═ Mc + Mc)/ms, and in fig. 3, the abscissa axis represents the ratio C/a (═ Mc + Mc)/ma). The vertical axis represents the relative value of the capacity coefficient (K), and is K/K0 which is the ratio of the capacity coefficient (K0) in the case of using a carbon material to which no quicklime powder is added.

When the relative value K/K0 of the capacity coefficient exceeds 1.2, it can be judged that the recarburization rate is significantly improved even if experimental unevenness or the like is subtracted. As shown in FIG. 2, when the ratio C/S is 0.6 to 2.7, the relative value K/K0 of the capacity coefficient exceeds 1.2 in many cases. In addition, as shown in FIG. 3, when the ratio C/A is 0.7 to 6.5, the relative value K/K0 of the capacity coefficient exceeds 1.2 in many cases. Further, it was confirmed that: when the ratio C/S is 0.6 to 1.9 and the ratio C/A is 0.7 to 5.0, the relative value K/K0 of the capacity coefficient exceeds 1.5, and the carburization rate is remarkably increased. However, as shown in fig. 2 and 3, if only one of the ratio C/a and the ratio C/S is considered, there is a condition that the relative value K/K0 of the capacity coefficient is 1.2 or less or 1.5 or less even in the above-described region. On the other hand, the relative value K/K0 of the capacity coefficient of the example in which the ratio C/S is 0.6 to 2.7 and the ratio C/A is 0.7 to 6.5 exceeds 1.2.

FIG. 4 shows SiO₂-CaO-Al₂O₃And (3) a phase diagram of the ternary system and a relation of an experimental result. In fig. 4, a case where the capacity coefficient relative value K/K0 exceeds 1.5 is set as "a-group", a case where the capacity coefficient relative value K/K0 exceeds 1.2 and is 1.5 or less is set as "b-group", and a case where the capacity coefficient relative value K/K0 is 1.2 or less is set as "c-group". In addition, the carbon material shown in table 1 to which the quicklime powder was not added was set to "group d".

Fig. 4 also shows a liquidus line at 1400 ℃, and lines indicating C/S of 0.6, 1.9, 2.7, C/a of 0.7, 5.0, and 6.5. As a result, the "group b" is present only in the region surrounded by C/S of 0.6, C/S of 2.7, C/a of 0.7, and C/a of 6.5, and the "group a" is present only in the region surrounded by C/S of 0.6, C/S of 1.9, C/a of 0.7, and C/a of 5.0. When either one of the ratio C/S and the ratio C/a deviates from the above-described region, the relative value K/K0 of the capacity coefficient does not exceed 1.2.

The region of the ratio C/A between the "group b" and the "group a" substantially coincides with the region where the composition which becomes a liquid phase at 1400 ℃ exists. On the other hand, the region having the ratio C/S of "group b" to "group a" partially overlaps with the region having the composition of the liquid phase at 1400 ℃, but the entire region is shifted. For the region where the ratio C/S is less than 0.6, it is presumed that: even in the composition which becomes a liquid phase at 1400 ℃, the viscosity is high, and the removal of the ash film by stirring does not effectively work. On the other hand, in the region where the ratio C/S is 1.3 to 2.7, although the composition is not a liquid phase, it is presumed that: the saturation of CaO causes desulfurization in the vicinity of the interface in the reducing field for forming the carbonaceous material, resulting in an increase in the rate of carburization.

In fact, the following tendency is shown: the larger the C/S ratio, the more the increase in the S concentration in the molten iron is suppressed. In addition, the following effects can be estimated: since CaO is present in excess, the opportunity of contact between the exposed ash and CaO is sufficiently ensured along with the dissolution of carbon in the carbonaceous material, and the composition of the ash film is likely to change. However, it is believed that: in the region where the ratio C/S exceeds 1.9 and is 2.7 or less, since the amount of unreacted quicklime which is solid is large and this unreacted quicklime inhibits contact between molten iron and the carbon material, the carburization rate is reduced as compared with the region where the ratio C/S is 1.9 or less. In addition, when the ratio C/S exceeds 2.7, the contact inhibition effect by the quicklime powder is enhanced, and the recarburization rate is not increased and is decreased in some cases as compared with the case where the quicklime powder is not added.

From the above experiments it is known that: in the case of the carbon additive of the present application, it is important to satisfy the conditions of 0.6. ltoreq. C/S.ltoreq.2.7 and 0.7. ltoreq. C/A.ltoreq.6.5, and in this range, the carbon increasing rate is significantly increased, and further, when the conditions of 0.6. ltoreq. C/S.ltoreq.1.9 and 0.7. ltoreq. C/A.ltoreq.5.0 are satisfied, the effect of increasing the carbon increasing rate is particularly large.

Next, the results of changing the stirring power density of the coal a in the same small-sized furnace are shown in fig. 5 and 6. As shown in fig. 5 and 6, the increase in the recarburization rate was observed in the same C/S region and the same C/a region as those in the case where ∈ was 0.08 kW/ton at all the stirring strengths of ∈ 0.02, 0.18, and 0.30 kW/ton. From the above results, it is clear that: when the conditions of 0.6. ltoreq. C/S.ltoreq.2.7 and 0.7. ltoreq. C/A.ltoreq.6.5, preferably 0.6. ltoreq. C/S.ltoreq.1.9 and 0.7. ltoreq. C/A.ltoreq.5.0 are satisfied, the effect of increasing the recarburization rate can be obtained regardless of the strength of stirring.

The ratio R of the quicklime contained in the additive material when the conditions of the ratio C/S and the ratio C/a as described above are satisfied can be calculated by the following procedure. SiO in ash₂Mass (ms) of (2) and Al in ash₂O₃The sum of the masses (ma) of (a) does not exceed the ash content in the carbon material contained in the carbon additive. Therefore, if the ratio of quicklime in the carbonaceous material is set to R (═ Mc/M) and the ratio of ASH in the carbonaceous material is set to (ASH), the following formula (5) is established.

ms + ma ≦ M × (1-R) × (ASH) formula (5)

Further, if C/(ms + ma) is multiplied on both sides of expression (5) and R.ltoreq.C is used, expression (6) below can be obtained.

R is equal to or less than C and equal to or less than (1-R) × (ASH)/{1/(C/S) +1/(C/A) } formula (6)

Here, the variable X is defined by the following formula (7).

X ═ (ASH)/{1/(C/S) +1/(C/a) } formula (7)

In this case, X monotonically increases with respect to (ASH), ratio C/S, and ratio C/A, respectively.

When formula (6) is modified and substituted for formula (7), the following formula (8) can be obtained.

R is less than or equal to 1/(1+1/X) formula (8)

Here, since the right side of the formula (8) monotonically increases with respect to X, the upper limit value of the ratio R of quicklime becomes larger as the ASH ratio (ASH), the ratio C/S, and the ratio C/a become larger. If substituting in the preferable ranges of the ratio C/S and the ratio C/A, the ratio R of the quicklime in the carbon material is about 19.9% at the maximum.

As described above, the content of quicklime can be suppressed as compared with the conventional one. Although there is an increase in cost due to the use of a mixing device of a carbon material and quicklime, not only a cost reduction due to a high carburization rate is produced, but also a cost reduction effect due to a reduction in clogging in a pipe or the like due to a moisture absorption effect of quicklime is secondarily produced. This greatly reduces the overall operation cost, and further promotes the use of low-grade carbon materials, thereby significantly reducing the cost of the carbon additive.

In this experiment, the mixed powder was used as a carburant, but the carburant may be obtained through a briquetting process such as briquetting. In the case of briquettes, the carbon material is closer to quicklime as an additive, and thus the removal effect by modification of the ash film becomes larger.

Further, if the additive can be fed from above the furnace by free fall, not only can the facility for gas conveyance be omitted, but also the restrictions on the particle size of the additive and the like can be alleviated, and the cost can be reduced. In consideration of this, the maximum particle size of the carbonaceous material as the carburization material is preferably set to 20mm or less in order to secure a contact area with molten iron and secure a carburization rate. However, when coal containing 10% or more of volatile components is used as the carbon material, the volatile components are volatilized by heating until the coal comes into contact with molten iron and become powder, and therefore, the carbon material is not limited to the carbon material having a maximum particle size of 20mm or less, and may be used as the carbon material having a maximum particle size of 100mm or less. Further, when the carbon material is added from above, if the particle size is too small, the carbon material cannot reach the molten iron and is discharged to the outside of the furnace together with the exhaust gas, thereby causing a loss, and therefore, the lower limit of the maximum particle size of the carbon material is preferably set to 0.2 mm.

In addition, when the amount of ash in the carbon material is large, even if the ash film is modified by mixing quicklime, the amount of the ash film becomes too large, and there is a possibility that the ash film cannot be efficiently removed from the interface. Therefore, the upper limit of ash content in the carbon material is set to 18 mass%. Further, the less ash content in the carbon material, the less the effect of mixing quicklime, and the more expensive the carbon material with less ash content, and the lower limit of the ash content in the carbon material is set to 5 mass% from the viewpoint of cost compatibility.

The additive mixed with the carbon material is quicklime containing CaO as a main component. Even if CaCO such as limestone is used₃The main component is added into the furnace as additiveAnd CO is heated₂Since the CaO is separated from the binder, the same effect as that of the quicklime can be expected in principle, but the expected effect cannot be obtained in practice. The reason for this is believed to be due to: because of CO₂Since the desorption reaction is an endothermic reaction and the carburization reaction is also an endothermic reaction, the ash film cannot be sufficiently heated, and the ash film has insufficient fluidity and cannot be effectively removed.

The content of CaO in the quicklime mixed with the carbon material is preferably 80 mass% or more, and more preferably 90 mass% or more.

The particle size of the added quicklime is preferably set to 10mm or less in maximum particle size in order to exert an effect by uniformly dispersing the quicklime on the surface of the carbon material. More preferably, the quicklime is in the form of powder and has a maximum particle size of 1mm or less.

Next, a description will be given of a method of carburizing using the above-described carburizing material. In the example shown in fig. 1, an ac electric furnace is set, but if the following points 2 are common, the electric furnace is not limited to the ac electric furnace shown in fig. 1: supplying a carbon material from above the molten iron surface; and can be stirred with a gas. In the present embodiment, an ac electric furnace, a dc electric furnace, or a ladle is assumed as a refining vessel for performing the carburization under the condition of weak stirring strength. It is not assumed that the recarburization is performed under strong stirring conditions using a converter type refining apparatus.

In the principle of mixing quicklime into a recarburizing material to modify an ash film, if molten slag comes into contact with the recarburizing material, the effect of mixing quicklime is reduced. Therefore, when a molten slag layer is present on the molten iron, it is preferable that the molten iron is stirred by blowing a bottom-blowing gas from a bottom-blowing tuyere to partially expose the molten iron surface, and the additive is introduced so as to directly contact the molten iron surface. The type of the bottom-blown gas is not limited, and the bottom-blown gas may be sprayed instead of bottom-blown gas as a stirring method using a gas. Solid components may also be present in the molten slag layer.

In the example shown in fig. 1, the additive is supplied from the lance 3 together with the carrier gas, but the additive may be supplied from a plurality of lances or may be supplied by free fall. Further, a molten and remaining chill source may be present when the additive is charged. The S concentration of the molten iron to be carburized is preferably set to 0.5 mass% or less from the viewpoint of workability in the removal of S.

Examples

Next, examples for confirming the operation and effect of the carbon additive of the present application will be described. The data shown in the present embodiment is merely an example showing an example to which the present application is applied, and the application range of the present application is not limited thereby.

An arc type bottom-blowing electric furnace (electric furnace 1) of an actual machine capable of melting 90 tons of molten iron as shown in fig. 1 was used, and the iron scrap was melted by arc heating from a graphite electrode (electrode 2). Further, N is blown from the bottom-blowing tuyere 4₂And (4) stirring the molten iron and measuring the temperature of the molten iron. The number of bottom-blowing tuyeres was 6, and the gas flow rates from the tuyeres were adjusted to be equal. Thereafter, a carbon additive was fed from above through the free fall from the lance 3, and temperature measurement and sampling were performed at regular intervals while controlling the stirring intensity, and the molten iron temperature and the C concentration were measured to calculate the capacity coefficient K from the above equation (3). The lance 3 is provided directly above 1 of the bottom-blowing ports 4, exposes the molten iron surface by stirring with the bottom-blowing gas, and injects a carburizing material into the exposed portion. The stirring power density at this time was set to be ∈ 0.18 kW/ton. In addition, arc energization is performed under some conditions in the carburization. The carbonaceous material was a mixture of a carbonaceous material having a maximum particle size of 20mm and quicklime powder having a maximum particle size of 1mm (CaO content in quicklime: 90 mass%), and the carbonaceous materials used were coal a and coal C shown in table 1. In the reference example, a recarburizing material of only a carbon material, which was not mixed with quicklime powder, was used. The main operating conditions are shown in table 2.

Regarding the "determination" in table 2, it is considered that the recarburization rate is improved by mixing the quicklime powder if the relative value K/K0 in the case where the capacity coefficient K0 of the reference example to be compared is set to 1.0 exceeds 1.0, as compared with the reference example under the same conditions (the same carbon species, the same temperature) except that the quicklime powder is mixed. When the relative value K/K0 of the capacity coefficient exceeds 1.2, it is determined that the carburetion rate is significantly increased and set as Y (acceptable), and when it is 1.2 or less, it is determined that no significant increase is seen and set as N (unacceptable). Specifically, example 3 was compared with reference example 9, and example 4 was compared with reference example 8, except that the comparison was made with reference example 7.

[ Table 2]

In examples 1 to 4 shown in Table 2, the ratio C/S and the ratio C/A satisfy the ranges of 0.6 to 2.7 and 0.7 to 6.5, respectively. In this case, the relative values of the capacity coefficients are all Y, which is a good result. If example 4 is compared with reference example 8, it shows: even when coal C having a large amount of ASH is used, by using a carburant in which quicklime powder is mixed in an appropriate ratio, a significant increase in the carburant rate can be achieved over coal a having less ASH and volatile components than coal C. In example 3, the molten iron temperature was 1600 ℃, but a significant increase in the recarburization rate was observed by mixing quicklime powder with the recarburizing material in the same manner as in the case of 1500 ℃.

In comparative example 5, the ratio C/A is in the range of 0.6 to 2.7, but the ratio C/S is out of the range of 0.7 to 6.5. In this case, the relative value of the capacity coefficient was 1.17 even compared with reference example 7, and no significant increase in the carburization rate was observed.

On the other hand, the ratios C/S and C/A of comparative example 6 are out of the above ranges (C/S: 0.6 to 2.7, C/A: 0.7 to 6.5). In this case, the relative value of the capacity coefficient was 0.42, and the carburetion rate was decreased, as compared with reference example 7.

As described above, in the examples of the present application, it was confirmed that: the carbon deposition rate can be accelerated even when a carbon material having a high ASH content and a low solubility is used.

The present application has been described above with reference to the embodiments, but the present application is not limited to the configurations described in the above embodiments, and includes other embodiments and modifications that are considered within the scope of the items described in the claims.

Description of the symbols

1 electric stove

2 electrode

3 spray gun

4 bottom blowing tuyere

5 molten iron

The disclosure of japanese patent application 2018-230108, filed 12, 7, 2018, is incorporated by reference in its entirety. All documents, patent applications, and technical standards described in the present specification are incorporated by reference into the present specification to the same extent as when each document, patent application, and technical standard is specifically and individually described.

Claims

1. A carburizing material, which is a carburizing material for carbonizing molten iron contained in an electric furnace or a ladle,

It is a mixture of a carbon material and quicklime having an ash content of 5% by mass to 18% by mass, and satisfies the conditions of the following formulas (1) and (2),

0.6≤(mc+Mc)/ms≤2.7 Equation (1)

0.7≤(mc+Mc)/ma≤6.5 Equation (2)

Wherein, mc represents the mass of CaO in the carbon material, ms represents the mass of SiO ₂ in the carbon material, ma represents the mass of Al ₂ O ₃ in the carbon material, and Mc represents the mass of the quicklime.

2. The recarburizer according to claim 1, wherein the mixture satisfies the conditions of the following formula (1A) and formula (2A),

0.6≤(mc+Mc)/ms≤1.9 Formula (1A)

0.7≤(mc+Mc)/ma≤5.0 Formula (2A)

3. A carburizing method using the carburizing method of claim 1 or claim 2,

In the electric furnace or the ladle, the recarburizing material is added to the molten iron surface formed by blowing gas and stirring the molten iron to increase carbonization.

The recarburizing method according to claim 3, wherein the recarburizing material is added by being charged from a spray gun toward the molten iron surface.